Between ages 3 and 5, children learn to form longer sentences. This enables them to express themselves with more detail, and thus be better understood.
The Sentence Train was specially designed to help children expand their sentences by adding time or place markers. Around age 4½ children are generally comfortable using this type of marker, but can still learn to use a richer variety of expansions.
The Sentence Train is based on an accepted principle of language acquisition: children learn the rules of language through repeated exposure to a range of examples. By creating opportunities for children to form sentences with markers of place or time, the game teaches children to assimilate this type of construction.
The Sentence Train also builds on children’s growing cognitive abilities. So around age 3, and sometimes earlier, children enjoy laughing at absurd situations, like "The boy is taking a bath in the kitchen." These silly situations are what make the game especially fun.